Ваша формула [B3 = IF (RIGHT (R3,3) = "K09", TRIM (LEFT (W3,35)), B2)] будет возвращать ошибку для каждой строки, пока первый раз R не закончится в K09.Однако, если это то, что вы хотите, то
let Source = Table.FromList({
[SAP segment name="L04K29", Application data ="ABCDEFGHIJKLMNOP12345VWXYZabcdefghijklmnopqrstuvwxyz"] ,
[SAP segment name="R03L09", Application data ="abcdefghijklmnop67890qrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"] ,
[SAP segment name="L04K09", Application data ="ABCDEFGHIJKLMNOP987654QRSTUVWXYZabcdefghijklmnopqrstuvwxyz"] ,
[SAP segment name="L04K09", Application data ="ABCDEFGHIJKLMNOPQR321254STUVWXYZabcdefghijklmnopqrstuvwxyz"] ,
[SAP segment name="R03G09", Application data ="abcdefghijklmnopqrst87562uvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"] ,
[SAP segment name="L04K09", Application data ="ABCDEFGHIJKLMNOPQRSTU45265VWXYZabcdefghijklmnopqrstuvwxyz"]
}, Record.FieldValues, {"SAP segment name", "Application data"}),
#"Added Custom" = Table.AddColumn(Source, "Custom", each if Text.End ([SAP segment name],3) = "K09" then Text.Trim(Text.Start([Application data],35)) else null),
#"Filled Down" = Table.FillDown(#"Added Custom",{"Custom"})
in
#"Filled Down"